Asphaltic products have been produced in various forms, with the primary uses of asphalt being in paving and in roofing products. The common source of asphalt is the residue or bottoms from the petroleum refining industry. This asphalt must be further refined or processed by air blowing (oxidizing) in order to raise the softening point and increase the stiffness to make useful products for roofing and specialty asphalt products. Some asphalt products have improved properties because of the addition of natural or synthetic rubbers or other organic additives.
While asphalt itself has many beneficial properties, it lacks inherent tensile strength and integrity. Therefore many asphalt products are reinforced with such materials as glass fibers or organic fibers such as polymer fibers, and have fillers such as ground limestone. For example, asphalt roofing shingles are based on an interior web or carrier of a wet process glass fiber mat, and the asphalt itself contains about 65 percent by weight ground limestone filler. Other fillers used in asphalt products include carbon black, finely ground tires, clay, ground glass and beads of various inorganic or organic materials.
One of the problems with reinforcing asphalt is that it is often difficult to integrate the reinforcement material into the asphalt matrix, particularly in a uniform manner. Typically, integrating the asphalt and the reinforcement is accomplished by fixing the reinforcement material into a mat or web, and applying the asphalt in molten form, as is the case in manufacturing asphalt roofing shingles. Shingle manufacturing consists of running a continuous wet process glass fiber mat into a bath of molten asphalt to cause a coating on both sides of the mat as well as filling the interstices between the individual glass fibers. This process is limited in that it can only apply a relatively uniform coating, similar to a film. It would be advantageous to be able to apply layers of asphalt into various products where the layers are not films, but are rather porous mats or other types of non-uniform layers. Also, the coating process requires assembly of the ultimate product at a-manufacturing facility with a liquid asphalt coater. It would be advantageous to be able to assemble products containing asphalt layers at field locations, such as at a road repair site.
Another known method for integrating asphalt with reinforcements is to mix the asphalt with loose or particulate reinforcement materials. Such mixing requires significant energy and capital equipment, and is not always successful in providing a uniform mix of asphalt and reinforcement. It would be advantageous to be able to uniformly intermix or integrate asphalt with reinforcement materials which are in an unfixed or loose form, rather than bound into a fixed product such as a mat. Also, it would be advantageous to be able to introduce the asphalt itself into various products in forms other than as a liquid.
Numerous reinforcement layers have been used for reinforcing highway systems. Such well known reinforcement layers include glass fibers in mat form, either woven or nonwoven, asphalt impregnated mats, mats of organic materials, such as polyester fibers, mats in the form of an open weave or grid, and layers of glass fibers or other reinforcement fibers. These reinforcement layers are applied to the roadway beneath subsequently applied bituminous aggregate asphalt layers to reinforce the bituminous aggregate. Such reinforcement layers are typically used in locations where the underlying pavement has cracked, and the highway system is being repaired. Reinforcement layers can also be used on the entire highway for repaving or as original construction. Also, reinforcement layers can be used for special applications such as bridge decks. It is well known to use a tack coat on any of these highway reinforcement products to secure the reinforcement product to the roadway prior to applying the paving layer.
One of the problems with currently available highway reinforcement products is that assembling various layers making up the highway reinforcement is a time consuming and costly process. Also, it is difficult to accurately meter out the asphalt layers in such products. Further it is not easy to fully integrate reinforcement layers of the highway reinforcement product with the asphalt without completely impregnating the reinforcement layer in a molten asphalt bath. Finally, it would be advantageous to be able to produce highway reinforcement products with higher strength without having to increase the materials used.